FCC separator without a reactor

ABSTRACT

This invention is directed to a process for fluid catalytic cracking, including, fluidizing a hydrocarbon stream in a riser, cracking the hydrocarbon stream with catalyst in the riser to produce a cracked stream and spent catalyst, separating the cracked stream and the spent catalyst in a primary separator to obtain a cracked stream with a first concentration of spent catalyst, and transporting the cracked stream with the first concentration of spent catalyst through a conduit to a multi-cyclone separator comprising multiple cyclones extending through a tube sheet to obtain a cracked stream with a second concentration of spent catalyst. The invention is also directed to an apparatus for catalytic cracking including a riser, a primary separator, a disengagement vessel surrounding the primary separator to collect the catalyst, a gas conduit having a first end in fluid connection with the disengagement vessel, and a multi-cyclone separator comprising a plurality of cyclones.

BACKGROUND OF THE INVENTION

This invention is directed to a method and an apparatus forcatalytically cracking heavy hydrocarbons and separating the spentcatalyst from the cracked product stream.

DESCRIPTION OF THE PRIOR ART

Fluid catalytic cracking (FCC) is a catalytic conversion process ofheavy hydrocarbons into lighter hydrocarbons accomplished by contactingthe heavy hydrocarbons in a fluidized reaction zone with a catalystcomposed of finely divided particulate material. Most FCC units now usezeolite-containing catalyst having high activity and selectivity.

The basic components of the FCC process include a riser, a reactorvessel for disengaging spent catalyst from product vapors, a regeneratorand a catalyst stripper. In the riser, the hydrocarbon feed contacts thecatalyst and is cracked into a product stream containing lighterhydrocarbons. In the riser, regenerated catalyst and the hydrocarbonfeed are transported upward by the expansion of the gases that resultfrom the vaporization of the hydrocarbons, and other fluidizing mediums,upon contact with the hot catalyst. Upon contact with the catalyst thehydrocarbon feed is cracked into lower molecular weight products. Cokeaccumulates on the catalyst particles as a result of the crackingreaction and the catalyst is then referred to as “spent catalyst.” Thespent catalyst must be removed from the cracked products to reducecatalyst losses from the system and to avoid contamination of theproducts. High temperature regeneration burns coke from the spentcatalyst. The regenerated catalyst is then returned to the reactionzone. Spent catalyst is continually removed from the reaction zone andreplaced by essentially coke-free catalyst from the regeneration zone.

The current state of the art FCC reactor design includes a riserexternal to the reactor vessel that continues into the reactor vesseland typically terminates in a primary separation device. After leavingthe primary separation device the reactor vapors and entrained catalystenter into a secondary catalyst separation device, which may becyclones. The reaction vapors leaving the cyclones are further combinedtypically in a plenum chamber before exiting the reactor and flowing tothe main column. The outlet of the internal riser, the primaryseparation device, the cyclones and the plenum chamber are all containedwithin a large reactor vessel. The reactor is very large and thereforecostly to manufacture and construct. The reactor vessel also adds coststo the FCC operation due to the amount of steam required for catalystfluidization and dome steam for reactor vessel purging. It is preferableto reduce the amount of utilities necessary to maintain the reactoroperation.

SUMMARY OF THE INVENTION

This invention is directed to a process for fluid catalytic cracking,including, fluidizing a hydrocarbon stream in a riser, cracking thehydrocarbon stream with catalyst in the riser to produce a crackedstream and spent catalyst, separating the cracked stream and the spentcatalyst in a primary separator to obtain a cracked stream with a firstconcentration of spent catalyst, and transporting the cracked streamwith the first concentration of spent catalyst through a conduit to amulti-cyclone separator comprising multiple cyclones extending through atube sheet to obtain a cracked stream with a second concentration ofspent catalyst. The invention may also include regenerating andrecycling the regenerated catalyst to the riser. The invention may alsoinclude collecting the spent catalyst in a collection vessel below thethird stage separator after the further separating step. The furtherseparating step may include providing differential pressure in the thirdstage separator. In another aspect of the invention, the spent catalystmay be in a disengagement vessel encircling the primary separator priorto the regenerating step.

In still another aspect, the invention is directed to an apparatus forcatalytic cracking including a riser, a primary separator locatedproximate an outlet end to substantially separate the catalyst from thecracked stream, a disengagement vessel surrounding the primary separatorto collect the catalyst, a gas conduit having a first end in fluidconnection with the disengagement vessel, and a multi-cyclone separatorcomprising a plurality of cyclones extending through a tube sheet and asecond end of the gas conduit in fluid connection with the multi-cycloneseparator. The collection vessel may be flowably connected to thedisengagement vessel at a position below the primary separator.

In another aspect of the invention, the disengagement vessel has a topabove the outlet end and the top and the multi-cyclone separator areconnected by a conduit that redirects flow by about 180 degrees. Theinvention may also include an outflow line for channeling the crackedstream leaving the multi-cyclone separator and a pressure controller onthe outflow line creates differential pressure in the separator. Thedisengagement vessel may also include baffles that encircle the riserbelow the primary separator. The collection vessel may be flowablyconnected to the disengagement vessel at a position above the baffles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross-sectional elevation view of an FCC apparatus with ariser, a primary separator, and a multi-cyclone separator.

FIG. 2 is a cross-sectional elevation view of the multi-cycloneseparator shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

An FCC reaction may occur without a reactor vessel and the spentcatalyst may be separated from the cracked stream first in primaryseparator 20 and then in multi-cyclone separator 30. Heavy hydrocarbonfeed may be added to riser 10 via feed injection nozzles 15. Thecracking reaction may be mostly completed in riser 10 and produce acracked stream. The spent catalyst and the cracked products may beseparated at primary separator 20 located on top of riser 10. Theseparated spent catalyst may travel downwardly through disengagementvessel 25 and into a regenerator 90. Catalyst may be regenerated in theregenerator 90 by combustion with air. The cracked stream with someentrained spent catalyst may be carried upwardly into a multi-cycloneseparator 30 for separating substantially all of the entrained spentcatalyst. The cracked stream may then go to a main column (not shown)for initiation of cracked product separation.

As shown in FIG. 1, a hydrocarbon feed stream may be fed to a riser 10at feed injection nozzles 15 and may be contacted and vaporized by hotregenerated catalyst entering through the nozzles 15 and fluidized by agas such as steam from a nozzle 17. The catalyst cracks the hydrocarbonfeed stream and a mixture of spent catalyst particles and gaseouscracked hydrocarbons exit discharge openings 23 (only one shown) inswirl arms 22 into a disengagement vessel 25. Tangential discharge ofgases and spent catalyst from the swirl arms 22 produce a swirlinghelical motion about the interior of the disengagement vessel 25,causing heavier catalyst particles to fall down a stripping section 26of the disengagement vessel 25. The spent catalyst particles may bestripped of entrained cracked vapors over baffles 27 with a strippingmedium such as steam entering from at least one stripping nozzle 24. Atleast about 90 wt-%, and preferably at least about 95 wt-%, of the spentcatalyst may be separated from the cracked stream by a primary separator20. The spent catalyst particles disengaged by the primary separator 20may be the first concentration of spent catalyst separated from thecracked stream.

Tangential discharge of cracked stream vapor and spent catalyst from theswirl arms 22 may produce a swirling helical motion about the interiorof the disengagement vessel 25 causing heavier catalyst particles tofall downwardly through the baffles 27 and a mixture of spent catalystentrained in vaporous cracked products to travel upwardly into atransport conduit 21 which makes a U-bend into a multi-cyclone separator30.

Continuing with FIG. 1, stripped spent catalyst from the strippingsection 26 of the disengagement vessel 25 may travel through a spentcatalyst pipe 28 regulated by a control valve 29 into the regenerator90. The spent catalyst may be distributed into a dense bed 92 by adistributor 94 where high temperatures in the presence of oxygen willcombust the coke from the catalyst particles and regenerate, or restore,the activity of the catalyst particles. The entrained regeneratedcatalyst may be separated from the regeneration gases by cyclones 93with the catalyst particles falling back towards the dense bed 92. Theregenerated catalyst may be returned to the bottom of the riser 10 by areturn conduit 98. Regeneration flue gas may exit the regenerator 90 bya flue gas outlet 100.

The temperature in the riser 10 may be between about 454° C. and about593° C. (between about 850° F. and about 1100° F.), preferably betweenabout 482° C. and about 566° C. (between about 900° F. and about 1050°F.), and more preferably between about 510° C. and about 538° C.(between about 950° F. and about 1000° F.). The regenerator 90 mayregenerate catalyst at between about 593° C. and about 896° C. (betweenabout 1100° F. and about 1500° F.), preferably between about 649° C. andabout 760° C. (between about 1200° F. and about 1400° F.), morepreferably between about 660° C. and about 732° C. (between about 1220°F. and about 1350° F.).

After the FCC reaction, the gaseous mixture of gaseous crackedhydrocarbons and entrained spent catalyst particles may leave thedisengagement vessel 25 and travel up and down the transport conduit 21and enter the multi-cyclone separator 30. The transport conduit 21 mayextend vertically upwardly from the disengagement vessel 25 and bendabout 90 degrees to extend horizontally and then bend about 90 degreesto extend vertically downwardly to connect to the top of themulti-cyclone separator 30. The transport conduit 21 may bend about 180degrees between the disengagement vessel 25 and the multi-cycloneseparator 30.

As shown in FIG. 2, the multi-cyclone separator 30 receives the gaseousmixture via a separator inlet 31. The multi-cyclone separator 30 maycontain numerous individual cyclones 53. Although only four cyclones 53are represented in FIG. 2, between about 10 and about 200 cyclones 53may be used depending on the size of the FCC unit. The separator inlet31 may face an upper tube sheet 56 that retains top ends 54 of thecyclones 53. The upper tube sheet 56 at least partially defines an inletchamber 55 and limits communication between the inlet chamber 55 and therest of the multi-cyclone separator 30. The gaseous mixture may bedistributed via a diffuser 50 to the inlets 51 of the plurality ofcyclones 53 containing swirl vanes 52, which may be structures thatrestrict the passageway through which incoming gas can flow, therebyaccelerating the flowing gas stream. The swirl vanes 52 may also changethe direction of the gaseous mixture to provide a helical or spiralformation of gas flow through the length of cyclones 53. The spinningmotion imparted to the gaseous mixture sends the higher-density catalysttoward the wall of the cyclone 53. The catalyst falls down the cyclones53 and out of open bottom ends 58 into a solids chamber 57 definedbetween the upper tube sheet 56 and a lower tube sheet 59. In oneembodiment the bottom ends 58 are closed and the catalyst exits slotsformed in the wall of the cyclone 53. In another embodiment, the solidsoutlet tube 34 extends from the solids chamber 57 into a collectionvessel 35 and transports solids collected on the lower tube sheet 59into the collection vessel 35. As shown in FIGS. 1 and 2, the bottom ofthe multi-cyclone separator 30 may be defined by a hemispherical region32 which is a clean gas area. Essentially all of the catalyst istransferred out of the multi-cyclone separator by the solids outlet tube34.

Continuing with FIG. 2, clean gas, flowing down the center of cyclones53, passes through open-ended cyclone gas outlet tubes 72 below thelower tube sheet 59 and into a clean gas chamber 73. The combined cleangas stream, representing the bulk of the gaseous mixture fed to themulti-cyclone separator 30 then exits into a main column line 41. Thelower tube sheet 59 limits communication between the clean gas chamber73 and the solids chamber 57.

Referring back to FIG. 1, a differential pressure controller 40 on themain column line 41 regulates differential pressure across the uppertube sheet 56 and the lower tube sheet 59 to regulate flow through thesolids outlet tube 34. Catalyst level is regulated in a collectionvessel 35 by use of the slide valve 39 in a spent catalyst returnconduit 38. The differential pressure controller 40 keeps a slightlyhigher pressure in the multi-cyclone separator 30 than in the maincolumn line 41. The pressure difference drives the flow of catalyst downthe solids outlet tube 34. A transfer pipe 80 which connects thecollection vessel 35 to the main column line 41 acts to equalize thepressure between the collection vessel 35 and the main column line 41,so that gas and catalyst may flow through cyclones 53 and the spentcatalyst may be effectively separated from the cracked stream.

As shown in FIGS. 1 and 2, the bottom of the collection vessel 35 may bedefined by the hemispherical region 37. The shape of hemisphericalregion 37 may help collect catalyst, so it will not enter the clean gasin main column line 41 though line 80.

The underflow may be the portion of the vapor that may be directed tothe solids outlet tube 34 at the bottom of multi-cyclone separator 30.The amount of underflow corresponds to the amount of flow carrying thefines away from the clean cracked stream. The underflow rate may betypically between about 3 vol-% and about 5 vol-% of the total flowrate. In one instance the underflow would carry the catalyst into thecollection vessel 35 where the level would be controlled by a slidevalve 39 on the conduit 38. The underflow vapor would then turn back upthe vessel 35 and into the transfer pipe 80 to the main column line 41to the main column (not shown). There may be a critical flow orifice(not shown) on the main column line 41. The critical flow orifice may bea Venturi-type flow instrument that is naturally restrictive and allowsa predetermined flow without the use of a control valve. The conduit 38preferably returns separated catalyst from multi-cyclone separator 30back to disengagement vessel 25. The catalyst then falls down strippingsection 26 though baffles 27.

After passing through the multi-cyclone separator 30, at least about 98wt-%, and in one embodiment at least about 99 wt-%, of entrained spentcatalyst may be removed from the cracked stream. The catalyst recoveredfrom the multi-cyclone separator 30 may be a second concentration ofcatalyst recovered.

The amount of steam required for an FCC unit without a reactor may besignificantly less than in a traditional FCC unit. In a traditional FCCunit, acceleration steam input to the steam distributor 17 at the baseof the riser 10, feed steam to the feed distributors 15 in the riser 10,stripping steam for stripping spent catalyst in the stripping section 26prior to regeneration, fluidization steam to direct catalyst from areactor vessel to a regenerator, and dome purge steam to purge thereactor shell are all necessary steam streams. In the FCC unit disclosedin FIG. 1, acceleration, feed and stripping steam are necessary, butthere may be no need for fluidization steam and dome purge steam becausethere is no reactor vessel. Along with the elimination of thefluidization and purge steams, the respective steam control valves mayalso be eliminated. Less instrumentation may be necessary than in atraditional FCC unit because not as many thermocouples may be needed inan FCC unit without a reactor vessel. The number of thermocouples neededin the new FCC unit may be between about 5 and about 8, and in oneembodiment about 6. Furthermore, the catalyst level and density taps andcyclone differential pressure taps may not be needed in an FCC unitwithout a reactor vessel. Without all the pressure taps, the dry-gaspurge points may be decreased by at least about 30%, and in oneembodiment by at least about 50%.

In the new FCC unit design, no dead areas in the unit may accumulatecoke deposits and cause maintenance problems. In a traditional FCC unit,there may be dead spaces in the reactor and large expansion joints thatget covered with coke in normal operation conditions. In the new FCCunit, about 100% of the riser 10, the primary separator 20, thedisengagement vessel 25, the multi-cyclone separator 30, and thecollection vessel 35 may be activated with flowing materials, so no cokedeposits can accumulate.

Furthermore, the catalyst inventory to the new FCC system may be reducedbecause there may be no longer a reactor so the entire volume of the FCCunit may be reduced. The normal operating volume of catalyst necessaryfor the reactor cyclones and for the reactor dilute phase may bereduced. In one embodiment, a traditional FCC unit may utilize about181,437 kg (about 200 tons). In the same embodiment, the FCC unitutilizing this invention may utilize about 154,221 kg (about 170 tons).For a traditional FCC unit, the new design should decrease the totalcatalyst inventory by between about 18,140 kg (about 20 tons) and about45,360 kg (about 50 tons), and in one embodiment about 27,200 kg (about30 tons). The decrease may be between an about 10 and an about 20 wt-%reduction in catalyst inventory, and in one embodiment about 15 wt-%reduction in catalyst inventory. Not only does this catalyst inventorydecrease lead to decrease in initial catalyst loading costs, but it hasthe additional advantage of requiring less additives, such as NOxreduction, SOx reduction and propylene producing additives, to be addedto the system to bring base catalyst loading up to design for theindividual additives.

The invention claimed is:
 1. A process for fluid catalytic cracking,comprising: fluidizing a hydrocarbon stream in a riser; cracking saidhydrocarbon stream with catalyst in said riser to produce a crackedstream and spent catalyst; separating said cracked stream and said spentcatalyst in a primary separator to obtain a cracked stream with a firstconcentration of spent catalyst; and transporting said cracked streamwith said first concentration of spent catalyst through a conduit to amulti-cyclone separator comprising multiple cyclones extending through atube sheet to obtain a cracked stream with a second concentration ofspent catalyst.
 2. The process according to claim 1, further comprisingregenerating said spent catalyst to provide regenerated catalyst andrecycling said regenerated catalyst to said riser.
 3. The processaccording to claim 2, further comprising stripping said spent catalystin a disengagement vessel encircling said primary separator prior tosaid regenerating step.
 4. The process according to claim 1, furthercomprising collecting said second concentration of spent catalyst in acollection vessel below said multi-cyclone separator after obtainingsaid cracked stream with said second concentration of spent catalyst. 5.The process according to claim 1, further comprising providing adifferential pressure in said multi-cyclone separator.